Influence of extensive muscle injury on fracture healing in rat tibia.

Abstract

The treatment of tibial fractures associated with severe soft tissue injury remains a challenge. The objective of our experiment was to ascertain the influence of standardized muscle injuries on fracture healing in a nailed rat tibial fracture model. We hypothesized that a severe crush injury of leg muscles might not be as deleterious to fracture healing as total loss of a large muscle segment. A randomized study in male Wistar rats with a diaphyseal osteotomy. Three separate, but complementary experiments were done in 51 rats. The first experiment involved 30 rats randomly assigned to three increasingly severe soft tissue interventions in a nailed tibial osteotomy model. The second experiment involved 14 rats divided into two groups to study blood flow measurements of the muscle envelope after soft tissue injury. Seven rats were used in the third experiment to provide biomechanical data and dimensions of the rat tibia. The protocol for the first experiment was intramedullary nailing after a middiaphyseal osteotomy of the left tibia. In group A, the soft tissue injury was minimal, while the muscles in the anterolateral compartment were crushed in group B. Resection of the anterolateral compartment muscles, resulting in only skin coverage at the fracture site, was performed in group C. The fibular nerve was resected in all three groups so that the animals were non-weight bearing on the operated extremity. At 4 weeks, the healing bones in each group were studied clinically, radiographically, and biomechanically. Radiographs in two planes revealed a clearly visible fracture line in the three intervention groups at 4 weeks. The callus area following muscle resection in group C was significantly reduced compared with the minimal soft tissue injury in group A. Biomechanically, resection of the anterolateral compartment muscles in group C reduced maximum bending load and fracture energy compared with fractures with minimal soft tissue injury in group A, while bending rigidity and fracture energy was reduced compared with muscle crush in group B. No difference in mechanical characteristics was detected between the healing bones in groups A and B. This animal study indicates that crushing of the leg muscle envelope with reduced blood flow does not influence the quality of bone healing at 4 weeks to a significant degree. Resection of a large muscle segment impairs tibial fracture healing significantly.